FastAPI — Modern, High-Performance Python Web APIs

# 1. Install FastAPI with the standard CLI and Uvicorn extras
pip install "fastapi[standard]"

# 2. Run your application in development mode with auto-reload
fastapi dev main.py

from fastapi import FastAPI

# 1. Instantiate the FastAPI application object
app = FastAPI(title="Inventory API")

# 2. Path operation decorator (@app.get) + Path operation function
@app.get("/")
def read_root():
    # Returning a Python dictionary automatically serializes to application/json!
    return {"status": "online", "framework": "FastAPI"}

@app.get("/api/health")
def health_check():
    return {"healthy": True, "version": "1.0.0"}

from fastapi import FastAPI
from pydantic import BaseModel

class UserPayload(BaseModel):
    name: str
    email: str

app = FastAPI()

# 1. PATH PARAMETER: Found in the URL path string {user_id}
@app.get("/users/{user_id}")
def get_user(user_id: int):
    return {"user_id": user_id}

# 2. QUERY PARAMETERS: Not in path, simple type (e.g. str, int, bool)
@app.get("/users")
def list_users(limit: int = 10, active_only: bool = True):
    # Matches GET /users?limit=25&active_only=false
    return {"limit": limit, "active_only": active_only}

# 3. REQUEST BODY: Declared as a Pydantic BaseModel class
@app.post("/users")
def create_user(payload: UserPayload):
    # Parsed from incoming JSON body stream
    return {"created_user": payload.name, "email": payload.email}